Indeed. Or columns 11 and 12 of BED files (genomics). Near on the agenda is a fast file loader straight into data.table and list columns (dual-delimited files such as BED).
I don't believe SQL has an analogous concept to list columns? To achieve that people may be using comma delimited strings in varchar columns, I guess. On Wed, 2011-10-05 at 16:19 -0500, Branson Owen wrote: > Thank you very, very much Matthew. I think this is a very valuable (at > least to me), and unique feature for more powerful calculation. A very > useful application I can immediately think of is for options chains > and order book modeling. It's much easier to track and model the whole > option chains or order book for each time stamp or symbol, and also > save a lot of replicating time stamps and symbols. > > 2011/10/4 Matthew Dowle <[email protected]> > On Sun, 2011-10-02 at 15:14 +0800, Branson Owen wrote: > > > Oh, sorry, I was testing the syntax like: > > > > DT = data.table(A = 1:2, B = list('a', 2i)) > > > > It didn't work, and I though this feature has not been > implemented. > > Thank you for pointing it out with a good example. > > > Natural to assume that should work. Now in 1.6.7 : > > o data.table() now accepts list columns directly rather than > needing to add list columns to an existing data.table; > e.g., > > DT = data.table(x=1:3,y=list(4:6,3.14,matrix(1:12,3))) > > Thanks to Branson Owen for reminding. > > Accordingly, one item has been added to FAQ 2.17 > (differences > between data.frame and data.table) : > "data.frame(list(1:2,"k",1:4)) > creates 3 columns, data.table creates one list column" > > As before, list columns can be created via grouping; e.g., > > DT = data.table(x=c(1,1,2,2,2,3,3),y=1:7) > DT2 = DT[,list(list(unique(y))),by=x] > DT2 > x V1 > [1,] 1 1, 2 > [2,] 2 3, 4, 5 > [3,] 3 6, 7 > > and list columns can be grouped; e.g., > > DT2[,sum(unlist(V1)),by=list(x%%2)] > x V1 > [1,] 1 16 > [2,] 0 12 > > > > > _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
